This invention relates to transducers that convert mechanical energy into acoustical energy. More specifically, it relates in one form to a loudspeaker with a piezoelectric actuator and in another form to a flat film speaker compatible with a video display.
All acoustic transducers must supply the atmosphere with an alternating positive and negative pressure. In its simplest form a linear motor, whether electromagnetic, electrostatic or piezoelectric, actuates a diaphragm that is sometimes part of the motor itself.
The overwhelming majority of loudspeakers are electromagnetic transducers. Referred to as dynamic loudspeakers, this class has essentially remained unchanged since the 1920's. Electromagnetic motors have long linear travel. This attribute is used to move a relatively small rigid diaphragm (in the manner of a piston, or “pistonic” as the term is used in the loudspeaker art) over the long excursions needed for acoustic use. The tradeoff is the low efficiency of this action at a distance.
Electrostatic and piezo devices have a much higher electrical-to-mechanical coupling efficiency than dynamic loudspeakers. They have been used to a limited degree for many decades, but their theoretical high efficiency has been limited by their comparatively short linear travel. In the case of electrostatics, very large diaphragm structures, several feet long on each side, are needed to generate the required acoustic displacement—or they are simply built small enough to be of practical size, but limited to operation in the upper frequencies where long excursions are not needed. Piezoelectrics have the highest theoretical efficiency of all, but they have been relegated to the upper frequencies exclusively because of their comparatively small size and limited excursion.
It is therefore an object of this invention to provide a new class of mechanical-to-acoustical transducers, especially loudspeakers, that can employ any of the aforementioned actuators, but are particularly well suited to transforming the high efficiency, short linear travel of a piezo motor into a high-excursion, pistonic-equivalent diaphragm movement.
Another object of this invention is to provide a flat, film-type speaker for televisions, computer monitors, or the like where the display is viewed through the speaker.